PURPOSE: Computed tomographic colonography (CTC) has been suggested as a potential alternative to colonoscopy for screening patients at risk for colorectal cancer. A recent clinical trial prospectively evaluated the sensitivity of air contrast barium enema (ACBE), CTC, and colonoscopy in 614 such patients. The effectiveness and the cost-effectiveness of the three imaging modalities in this population is uncertain.

METHODS: We developed a Markov model to evaluate the costs and health benefits for investigation of the colon to detect colorectal cancer in patients with fecal occult blood, hematochezia, iron deficiency anemia, or a family history of colon cancer. Patients were initially examined with one of three modalities: colonoscopy, ACBE, or CTC. Patients with negative colonoscopy underwent repeat colonoscopy every 10 years, patients found to have >=6mm lesions underwent workup and then surveillance every 5 years. Patients in the ACBE and CTC strategies who screened positive underwent colonoscopy and then followed the strategy described above. Patients who had negative ACBEs or CTCs underwent repeat screening every 5 or 10 years respectively. Patients in whom lesions of <6mm were identified, did not undergo workup for their lesions although we modeled possible progression of these lesions. Based on trial data, for large (>=10mm) lesions, the per-patient sensitivity of colonoscopy, ACBE, and CTC was 98%, 48%, and 59% respectively. Per patient specificity was 99.6%, 90%, and 96%, for the same three modalities.

RESULTS: For a representative patient, the ACBE strategy was the least costly ($6373) but had the lowest quality-adjusted life expectancy (14.96 QALYs). The CTC strategy cost an incremental $1114 but gained 0.01 QALYs compared to ACBE. Colonoscopy was more accurate and less expensive than CTC and therefore dominated the CTC strategy. The incremental cost-effectiveness of colonoscopy compared with ACBE was $20,571/QALY. If the tests characteristics of CTC were equal to those of colonoscopy, the CTC strategy is still more expensive because positive CTC exams require followup with colonoscopy. If patient compliance with colonoscopy was reduced to less than 60%, CTC became an acceptable strategy.

CONCLUSIONS: Colonoscopy appears cost effective over a wide range of assumptions. However, current CTC does not appear to be an effective or economically favorable strategy compared to colonoscopy. Because CTC is rapidly evolving our analysis should be updated as significant technological advances are achieved.